similar names but totally different strains. red diamond refers to some early stage red-turq x leopard, which is kind of a striated fish with red spots. Red golden diamond is golden based solid red fish, which is basically a result of hybriding golden with brown-based red fish. There're already some very stable RGD lines as far as I know, while people are still improving it nowadays.
This is the original red diamond created by WWFF
http://homepage2.nifty.com/fukuyama/...ted%20Line.htm
my red golden diamond bought from Kenny/Forrest
http://forum.simplydiscus.com/showthread.php?t=76458
just my 2 cents...
-Xiaofei